Publications by authors named "Ji-Man Park"

82 Publications

Immediate loading protocols increase the risk of failure of implants placed by fully guided surgery in partially edentulous jaws: A randomized clinical trial.

Clin Implant Dent Relat Res 2021 Aug 26. Epub 2021 Aug 26.

Department of Periodontology, Research Institute for Periodontal Regeneration, Yonsei University College of Dentistry, Seoul, South Korea.

Aim: To compare the 1-year outcomes of immediate loading (IL) and delayed loading (DL) protocols for implants placed by fully guided surgery in partially edentulous jaws.

Materials And Methods: This study included 72 patients who received implant surgery with either IL (93 implants, 36 patients) or DL (94 implants, 26 patients). A prefabricated provisional prosthesis was delivered immediately for the IL group (86 implants, 32 patients) with the exception of 4 subjects in whom an initial torque of >20 Ncm and an implant stability quotient of >65 were not achieved, while all DL-group implants were loaded after 3 months. The 1-year implant survival rate estimated by intention-to-treat (ITT) and per-protocol (PP) analyses, and the marginal bone loss (MBL) estimated by cone-beam computed tomography were statistically evaluated (p < 0.05).

Results: The survival rate in the DL group was 100% at both patient and implant levels. With only 26 subjects with 78 implants surviving in the IL group, the survival rates were 69.4% and 83.4% at the patient and implant levels, respectively, in the ITT analysis, and 78.1% and 90.2% in the PP analysis. All intergroup differences in survival rates were statistically significant (p < 0.01). MBL was less than 0.1 mm in both groups (p > 0.05).

Conclusions: IL for implants placed by fully guided surgery in the partially edentulous jaws increased the probability of failure compared to 3-month DL. Regardless of when loading occurred, marginal bone levels remained stable.
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http://dx.doi.org/10.1111/cid.13042DOI Listing
August 2021

Immediate loading of fixed partial prostheses reconstructed using either tapered or straight implants in the posterior area: A randomized clinical trial.

Clin Implant Dent Relat Res 2021 Aug 11. Epub 2021 Aug 11.

Department of Periodontology, Research Institute for Periodontal Regeneration, Yonsei University College of Dentistry, Seoul, South Korea.

Background: In immediately loaded implants within 72 h after the implant placement in the unilaterally and partially edentulous ridge, primary stability is considered critical, which can be influenced by the design of the implant fixture.

Purpose: To determine the outcomes at 1 year after the immediate loading of multiunit fixed partial prostheses over either tapered implants (TIs) or straight implants (SIs) in the posterior region.

Materials And Methods: Forty-eight patients (24 patients, 52 implants in TI group; 24 patients, 50 implants in SI group) were included for the study. Except for the one SI group patient whose two implants showed the insertion torque less than 30 Ncm, provisional prostheses designed and fabricated from intraoral scan data obtained immediately after implant surgery were delivered to rest of the 47 subjects at 3-7 days. After a year, the survival rate was estimated by intention-to-treat (ITT) and per-protocol (PP) analyses, and marginal bone loss (MBL) and implant stability were also analyzed statistically (p < 0.05).

Results: Survival rate at implant level in TI group was 96.2%, and that of SI group in the ITT analysis was 86.0%. Intergroup difference, however, was not statistically significant (p > 0.05). Insertion torque was significantly higher in TI group than SI group (47.12 ± 6.37 Ncm vs. 41.60 ± 9.77 Ncm; p < 0.05). MBLs of both groups were less than 0.1 mm at 1-year follow-up and was similar between two groups (p > 0.05).

Conclusions: Immediate loading of fixed partial prostheses after TI and SI placement showed reliable outcomes in the partially edentulous posterior ridge. In terms of the initial mechanical stability, the performance was superior for TIs than for SIs.
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http://dx.doi.org/10.1111/cid.13039DOI Listing
August 2021

Accuracy of Dental Implant Placement by a Novel In-House Model-Free and Zero-Setup Fully Guided Surgical Template Made of a Light-Cured Composite Resin (VARO Guide): A Comparative In Vitro Study.

Materials (Basel) 2021 Jul 19;14(14). Epub 2021 Jul 19.

Department of Periodontology, Research Institute for Periodontal Regeneration, Yonsei University College of Dentistry, Seoul 03722, Korea.

Background: This in vitro study mainly aimed to compare VARO Guide to the surgical guide fabricated by CAD/CAM (NAVI Guide) in terms of accuracy and efficacy of the implant surgery held in the dentiform model.

Methods: Twenty surgeons, 10 dentists in the beginner group and 10 dentists in the expert group, participated in the study. Each surgeon conducted fully guided surgery in dentiform models twice, once with VARO Guide (VG surgery) and the other time with a conventional type of templates, NAVI Guide (NG surgery). Based on the superimposition of presurgical and postsurgical STL files, the positional deviations between the virtually planned and actually placed implants and the time spent on presurgical preparation and surgical procedures were estimated and compared.

Results: All dimensional deviations were similar between the two groups ( > 0.05), and there was no significant difference between the expert and beginner groups regardless of the guide system. The total procedure time (mean (median)) of the VG surgery (26.33 (28.58) min) was significantly shorter than that of the NG surgery (378.83 (379.35) min; < 0.05). While the time spent only for the fully guided implant surgery (from the start of the surgical guide sitting onto the dentiform model to the final installation of the implant fixture) was comparable ( > 0.05), the presurgical preparation time spent on virtual implant planning and surgical guide fabrication in the VG surgery (19.63 (20.93) min) was significantly shorter compared to the NG surgery (372.93 (372.95) min; < 0.05).

Conclusions: Regardless of experience, both VG and NG surgery showed reliable positional accuracy; however, the total procedure time and the preparation time were much shorter in the VG surgery compared to the NG surgery.
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http://dx.doi.org/10.3390/ma14144023DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8304558PMC
July 2021

Assessment of tooth displacement during the cast-free digital processing of milled dentures.

J Prosthet Dent 2021 Jun 8. Epub 2021 Jun 8.

Private practice, Vallesaccarda, AV, Italy.

Statement Of Problem: Denture tooth displacement may have a significant impact on denture occlusion. This aspect has seldom been investigated, especially for digital denture processing techniques.

Purpose: The purpose of this clinical study was to evaluate the accuracy of tooth position with milled digital dentures processed without physical casts.

Material And Methods: Ten maxillary and 10 mandibular dentures designed from intraoral scans, milled, and processed without physical casts were investigated. The standard tessellation language (STL) files of the digitally designed dentures were compared with the scan of the dentures after processing (milling the denture base, milling teeth in a complete arch, and then bonding teeth into the base). The STL files were superimposed by using a surface-matching software program. After a preliminary alignment, the STL meshes were trimmed and reoriented; then, the final alignment was carried out by using the cameo surface. Six reference points (the mesiobuccal cusp on the most distal molar, the canine cusp, the middle of the incisal edge of the central incisor on both the left and the right side) were selected to measure tooth displacements along the X-, Y-, and Z-axes, corresponding (from the preliminary reorientation) to anteroposterior, mediolateral, and occlusal displacement, respectively. Tooth position accuracy was assessed by using median and interquartile range values. Univariate and multivariate statistical analyses were used to investigate the significance of the extent of displacements, as well as differences among displacement directions, reference teeth, side, and denture arch type (α=.05).

Results: Only the median (0.2 mm; interquartile range: 0.27 mm) occlusal displacement was significantly different from zero. A generalized estimated equation model addressing occlusal displacement as a dependent variable showed no significant effect of tooth type, side, or denture arch type, either alone or in combination.

Conclusions: The tooth position of both maxillary and mandibular milled digital dentures processed without physical casts was accurate in the anteroposterior and mediolateral directions. Occlusal displacement seemed to be within the range of clinical acceptability; its consistency throughout the arch allowed optimization or compensation at the design or manufacturing step.
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http://dx.doi.org/10.1016/j.prosdent.2021.04.028DOI Listing
June 2021

Correlation analysis of periodontal tissue dimensions in the esthetic zone using a non-invasive digital method.

J Periodontal Implant Sci 2021 Apr;51(2):88-99

Department of Periodontology and Dental Research Institute, Seoul National University School of Dentistry, Seoul, Korea.

Purpose: Direct intraoral scanning and superimposing methods have recently been applied to measure the dimensions of periodontal tissues. The aim of this study was to analyze various correlations between labial gingival thickness and underlying alveolar bone thickness, as well as clinical parameters among 3 tooth types (central incisors, lateral incisors, and canines) using a digital method.

Methods: In 20 periodontally healthy subjects, cone-beam computed tomography images and intraoral scanned files were obtained. Measurements of labial alveolar bone and gingival thickness at the central incisors, lateral incisors, and canines were performed at points 0-5 mm from the alveolar crest on the superimposed images. Clinical parameters including the crown width/crown length ratio, keratinized gingival width, gingival scallop, and transparency of the periodontal probe through the gingival sulcus were examined.

Results: Gingival thickness at the alveolar crest level was positively correlated with the thickness of the alveolar bone plate (<0.05). The central incisors revealed a strong correlation between labial alveolar bone thickness at 1 and 2 mm, respectively, inferior to the alveolar crest and the thickness of the gingiva at the alveolar crest line (G0), whereas G0 and labial bone thickness at every level were positively correlated in the lateral incisors and canines. No significant correlations were found between clinical parameters and hard or soft tissue thickness.

Conclusions: Gingival thickness at the alveolar crest level revealed a positive correlation with labial alveolar bone thickness, although this correlation at identical depth levels was not significant. Gingival thickness, at or under the alveolar crest level, was not associated with the clinical parameters of the gingival features, such as the crown form, gingival scallop, or keratinized gingival width.
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http://dx.doi.org/10.5051/jpis.2003460173DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8090792PMC
April 2021

An in vitro comparison of the marginal and internal adaptation of ultrathin occlusal veneers made of 3D-printed zirconia, milled zirconia, and heat-pressed lithium disilicate.

J Prosthet Dent 2021 Mar 16. Epub 2021 Mar 16.

Head, Division of Dental Biomaterials, Clinic of Reconstructive Dentistry, Center of Dental, University of Zurich, Zurich, Switzerland.

Statement Of Problem: Whether additively produced zirconia could overcome problems with conventional computer-aided design and computer-aided manufacture (CAD-CAM) such as milling inaccuracies and provide accurate occlusal veneers is unclear.

Purpose: The purpose of this in vitro study was to compare the marginal and internal fit of 3D-printed zirconia occlusal veneers with CAD-CAM-fabricated zirconia or heat-pressed lithium disilicate ceramic (LS2) restorations on molars.

Material And Methods: The occlusal enamel in 60 extracted human molars was removed, with the preparation extending into dentin. Occlusal veneers at a thickness of 0.5 mm were designed and manufactured according to their group allocation: 3DP, 3D-printed zirconia; CAM, milled zirconia; and HPR, heat-pressed LS2. The prepared teeth and restorations were scanned and superimposed, and the marginal and internal adaptation were measured 2- and 3-dimensionally; the production accuracy (trueness) was also measured. The comparisons of the group medians were performed with nonparametric methods and a pairwise group comparison (α=.05).

Results: Three-dimensionally printed zirconia revealed median outcomes of 95 μm (margin), 252 μm (cusp), 305 μm (fossa), and 184 μm (3D internal adaptation). CAM showed median values of 65 μm (margin), 128 μm (cusp), 203 μm (fossa), and 120 μm (3D internal adaptation). The respective values for the group HPR were 118 μm (margin), 251 μm (cusp), 409 μm (fossa), and 180 μm (3D internal adaptation). Significant differences (P<.001) between CAM and 3DP (cusp, fossa, 3D internal adaptation) and between CAM and HPR (all regions) were found, with the former group showing higher accuracies. The trueness showed median discrepancies of 26 μm (3DP), 13 μm (CAM), and 29 μm (HPR) with significant differences (P<.001) for the comparisons 3DP-CAM and CAM-HPR.

Conclusions: Three-dimensionally printed zirconia occlusal veneers produced by means of lithography-based ceramic manufacturing exhibit a marginal adaptation (95 μm) and a production accuracy (26 μm) similar to those of conventional methods.
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http://dx.doi.org/10.1016/j.prosdent.2020.09.053DOI Listing
March 2021

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition).

Autophagy 2021 Jan 8;17(1):1-382. Epub 2021 Feb 8.

University of Crete, School of Medicine, Laboratory of Clinical Microbiology and Microbial Pathogenesis, Voutes, Heraklion, Crete, Greece; Foundation for Research and Technology, Institute of Molecular Biology and Biotechnology (IMBB), Heraklion, Crete, Greece.

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.
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http://dx.doi.org/10.1080/15548627.2020.1797280DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7996087PMC
January 2021

In Vitro Comparison between Metal Sleeve-Free and Metal Sleeve-Incorporated 3D-Printed Computer-Assisted Implant Surgical Guides.

Materials (Basel) 2021 Jan 29;14(3). Epub 2021 Jan 29.

Department of Prosthodontics, Yonsei University College of Dentistry, Seoul 03722, Korea.

The present study aims to compare the accuracy of metal sleeve-free 3D-printed computer-assisted implant surgical guides (MSF group) ( = 10) with metal sleeve-incorporated 3D-printed computer-assisted implant surgical guides (MSI group) ( = 10). Implants of diameter 4.0 mm and 5.0 mm were placed in the left second premolars and bilateral first molars, respectively, using a fully guided system. Closed-form sleeves were used in teeth on the left and open-form sleeves on the right. The weight differences of the surgical guides before and after implant placement, and angular deviations before and after implant placement were measured. Weight differences were compared with Student's -tests and angular deviations with Mann-Whitney tests. Cross-sectional views of the insert parts were observed with a scanning electron microscope. Preoperative and postoperative weight differences between the two groups were not statistically significant ( = 0.821). In terms of angular deviations, those along the mesiodistal direction for the left second premolars were significantly lower in the MSF group ( = 0.006). However, those along the mesiodistal direction for the bilateral molars and those along the buccolingual direction for all teeth were not significantly different ( > 0.05). 3D-printed implant surgical guides without metal sleeve inserts enable accurate implant placement without exhausting the guide holes, rendering them feasible for fully guided implant placement.
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http://dx.doi.org/10.3390/ma14030615DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7866124PMC
January 2021

Dental students' perceptions on a simulated practice using patient-based customised typodonts during the transition from preclinical to clinical education.

Eur J Dent Educ 2021 Jan 29. Epub 2021 Jan 29.

Department of Prosthodontics, Yonsei University College of Dentistry, Seoul, Korea.

Purpose/objectives: Dental students experience difficulties during the transition from preclinical to clinical curriculum. In order to help the students to adapt to the clinical education programme, a simulated practice using patient-based customised models was introduced in this study to prepare for their first clinical practice.

Methods: This study included 45 third-year predoctoral students (D3 students) who were about to perform the preparation of a single crown abutment on their first patient. After practicing abutment preparation using simulated models and providing the actual treatment to their own patient, the students were surveyed to investigate their perceptions on the simulated practice using the 3D-printed customised typodont model. The statistical analysis of the quantitative data and the thematic analysis of the qualitative data were conducted.

Results: Regarding this simulation, more than 80% of the students gave positive feedback on their practice of (a) operative positions and postures, (b) finger rest, (c) occlusal reduction, (d) axial reduction and (e) proximal reduction. Student responses on the open-ended questions about how they perceived the usefulness of this simulation were categorised as "First clinical case," "Patient-based model" and "Realistic simulation environment." In addition, a number of improvements of the simulation were also suggested by the students including the typodont and the manikin.

Conclusions: This study gives insights into the significance of simulated practice using patient-based customised typodonts as a transitional education tool and its direction of development in the field of restorative treatments accompanied by irreversible tooth preparations.
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http://dx.doi.org/10.1111/eje.12672DOI Listing
January 2021

Trueness of ten intraoral scanners in determining the positions of simulated implant scan bodies.

Sci Rep 2021 01 28;11(1):2606. Epub 2021 Jan 28.

Department of Prosthodontics, College of Dentistry, Yonsei University, Seoul, 03722, South Korea.

Few investigations have evaluated the 3-dimensional (3D) accuracy of digital implant scans. The aim of this study was to evaluate the performance of 10 intraoral scanners (IOSs) (CEREC Omnicam, CEREC Primescan, CS 3600, DWIO, i500, iTero Element, PlanScan, Trios 2, Trios 3, and True Definition) in obtaining the accurate positions of 6 cylinders simulating implant scan bodies. Digital scans of each IOS were compared with the reference dataset obtained by means of a coordinate measuring machine. Deviation from the actual positions of the 6 cylinders along the XYZ axes and the overall 3D deviation of the digital scan were calculated. The type of IOSs and position of simulated cylindrical scan bodies affected the magnitude and direction of deviations on trueness. The lowest amount of deviation was found at the cylinder next to the reference origin, while the highest deviation was evident at the contralateral side for all IOSs (p < 0.001). Among the tested IOSs, the CEREC Primescan and Trios 3 had the highest trueness followed by i500, Trios 2, and iTero Element, albeit not statistically significant (p > 0.05), and the DWIO and PlasScan had the lowest trueness in partially edentulous mandible digital implant scans (p < 0.001).
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http://dx.doi.org/10.1038/s41598-021-82218-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7844289PMC
January 2021

Application of additive and subtractive manufacturing technology for a digitally fabricated removable partial denture after a partial maxillectomy: A clinical report.

J Prosthet Dent 2020 Nov 19. Epub 2020 Nov 19.

Professor, Department of Prosthodontics, College of Dentistry, Yonsei University, Seoul, Republic of Korea.

This clinical report describes the treatment of a patient with a large defect area in the maxillary central incisor, left lateral incisor, canine, and first premolar area after a partial maxillectomy. Computer-aided design and computer-aided manufacturing (CAD-CAM) techniques including rapid prototyping and milling were applied together to fabricate a removable partial denture.
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http://dx.doi.org/10.1016/j.prosdent.2020.06.030DOI Listing
November 2020

Trueness of intraoral scanners in digitizing specific locations at the margin and intaglio surfaces of intracoronal preparations.

J Prosthet Dent 2020 Nov 8. Epub 2020 Nov 8.

Associate Professor, Department of Prosthodontics, Yonsei University, College of Dentistry, Seoul, Republic of Korea. Electronic address:

Statement Of Problem: Studies evaluating the trueness of intraoral scanners (IOSs) at anatomic locations within an intracoronal preparation are lacking.

Purpose: The purpose of this in vitro study was to evaluate the trueness of digital scans obtained by IOSs at the margin and intaglio surfaces of intracoronal preparations.

Material And Methods: Six IOSs (CEREC Omnicam, E4D, FastScan, iTero, TRIOS, Zfx IntraScan) were used to obtain digital scans of various intracoronal preparations. Standard tessellation language (STL) data sets obtained from a reference scanner and each IOS were superimposed, and the deviation of the digital casts was assessed at multiple measuring points along the margin and intaglio surfaces of each preparation. The Kruskal-Wallis test and multiple Mann-Whitney tests were used to detect differences in trueness (α=.05).

Results: The overall median trueness values were lowest for TRIOS (23.9 μm), followed by Zfx IntraScan (24.6 μm), iTero (25.4 μm), FastScan (26.1 μm), CEREC Omnicam (26.9 μm), and E4D (77.5 μm). The greatest deviation was generally observed at the line angles between the preparation surfaces. The axiogingival line angle was the most error-prone location in the cavity preparations. An increased tendency to produce a more accurate impression was observed when the cavity had a greater width and more divergent walls.

Conclusions: The trueness of digital scans was influenced by the type of IOS and the location within a prepared cavity. The trueness decreased at the line angles between the preparation surfaces, particularly at the axiogingival line angle. Among the tested IOSs, E4D produced the least accurate digital scans.
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http://dx.doi.org/10.1016/j.prosdent.2020.09.019DOI Listing
November 2020

Assessment of Compatibility between Various Intraoral Scanners and 3D Printers through an Accuracy Analysis of 3D Printed Models.

Materials (Basel) 2020 Oct 4;13(19). Epub 2020 Oct 4.

Department of Prosthodontics, Yonsei University College of Dentistry, 50-1 Yonsei-ro, Seodaemun-Gu, Seoul 03722, Korea.

To assess the accuracy of various intraoral scanners (IOSs) and to investigate the existence of mutual compatibility that affects the accuracy between IOS and 3-dimensional (3D) printing using a scan quadrant model. For clinical implication, crown preparations and cavity design according to prosthetic diagnosis and treatment considerations must be acquired by a digital scanner. The selected typodont model was scanned using a reference scanner, from which reference (Ref) standard tessellation language (STL) data were created. Data obtained by scanning the typodont model with IOSs based on three different technologies were divided into three groups (CS3600, i500, and Trios3). Scanned data from the groups were divided into sub-groups of digital light processing (DLP), fused deposition modeling (FDM), and stereolithography apparatus (SLA), based on which 3D printed models (3DP) were fabricated. The 3DP dental models were scanned to obtain a total of 90 3DP STL datasets. The best-fit algorithm of 3D analysis software was used for teeth and arch measurements, while trueness was analyzed by calculating the average deviation among measured values based on superimposition of Ref and IOS and 3DP data. The differences between Ref and IOS (Ref-IOS), Ref and 3DP (Ref-IOS/3DP), and IOS and 3DP data (IOS-3DP) were compared and analyzed, while accuracy within each of the three main groups was assessed. For statistical analysis, the Kruskal-Wallis, Mann-Whitney , and repeated measures ANOVA test were used ( < 0.05). The major finding is that the mutual relationships between IOSs and 3D printers vary depending on the combination. However, i500 intraoral scanner and DLP 3D printer was the combination that showed the best trueness value.
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http://dx.doi.org/10.3390/ma13194419DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7579436PMC
October 2020

Dimensional accuracy and surface characteristics of 3D-printed dental casts.

J Prosthet Dent 2021 Sep 18;126(3):427-437. Epub 2020 Sep 18.

Professor, Department of Prosthodontics and Dental Research Institute, School of Dentistry, Seoul National University, Seoul, Republic of Korea. Electronic address:

Statement Of Problem: Although studies have reported the accuracy of 3D-printed dental casts, studies addressing cast distortion throughout the complete-arch range are lacking.

Purpose: The purpose of this in vitro study was to evaluate the dimensional accuracy of different areas in complete-arch casts made with various 3D printing methods.

Material And Methods: A computer-aided design (CAD) reference cast was modified from a mandibular cast by adding 6 cylinders in the canine, second premolar, and second molar locations and 3 spheres to define a coordinate system. A total of 50 casts were printed with 5 group materials, which included fused deposition modeling (FDM), digital light processing (DLP1 and DLP2), photopolymer jetting (Polyjet), and stereolithography (SLA). After scanning the 3D printed casts, the overall consistency was examined by superimposing them on the CAD reference cast and measuring the deviations. For dimensional accuracy, cylinder top coordinates were extracted from each printed cast, and X-, Y-, and Z-deviations and the 3D deviation were calculated by subtracting the coordinates of the CAD reference cast from the cast values. Statistical analyses were conducted by the Kruskal-Wallis test and the Mann-Whitney post hoc test (α=.05). Surface characteristics were examined with photographs and scanning electron micrographs.

Results: FDM showed more systemic deviations than DLP, Polyjet, and SLA from superimposing analysis (P<.01). In the X-axis, FDM and DLP showed contraction, while Polyjet and SLA showed expansion (P<.01). In the Y-axis, FDM showed forward deviations on the right side and DLP showed contraction (P<.01). Three-dimensional deviation at each cylinder location was lowest in the left canine region, and deviations increased with distance from this site in all groups. The qualitative features of casts varied among 3D printers in terms of shape, surface smoothness, and edge sharpness.

Conclusions: FDM and DLP casts tended to contract, whereas casts in the Polyjet and SLA groups expanded buccolingually and anterioposteriorly. Vertically, deviations were smaller than those in the other directions.
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http://dx.doi.org/10.1016/j.prosdent.2020.07.008DOI Listing
September 2021

Flexural Strength of 3D-Printing Resin Materials for Provisional Fixed Dental Prostheses.

Materials (Basel) 2020 Sep 8;13(18). Epub 2020 Sep 8.

Department of Prosthodontics and Dental Research Institute, Seoul National University Dental Hospital, School of Dentistry, Seoul National University, 101 Daehak-ro, Jongno-gu, Seoul 03080, Korea.

The clinical application of 3D-printed provisional restorations is increasing due to expansion of intraoral scanners, easy dental computer-aided design (CAD) software, and improved 3D printing speed. This study compared flexural strength of 3D-printed three-unit fixed dental prostheses with that of conventionally fabricated and milled restorations. A metal jig of two abutments and pontic space and an indenter for flexural strength measurement were fabricated. A three-unit fixed dental prosthesis was designed and manufactured using three additive manufacturing technologies, with subtractive manufacturing and a conventional method as controls. Digital light processing (DLP) group specimens were prepared from a polymethyl methacrylate (PMMA)-based resin and printed with a DLP printer. Stereolithography (SLA) group specimens were prepared from PMMA-based resin and printed with an SLA printer, and fused deposition modeling (FDM) group specimens were from a polylactic acid-based resin and printed with an FDM printer. Flexural strength was investigated using a universal testing machine, and the results were statistically analyzed. DLP and SLA groups had significantly higher flexural strength than the conventional group ( < 0.001). No significant difference was observed in flexural strength between DLP and SLA groups. The FDM group showed only dents but no fracture. The results of this study suggest that provisional restorations fabricated by DLP and SLA technologies provide adequate flexural strength for dental use.
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http://dx.doi.org/10.3390/ma13183970DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7559938PMC
September 2020

Changes in mucogingival junction after an apically positioned flap with collagen matrix at sites with or without previous guided bone regeneration: A prospective comparative cohort study.

Clin Oral Implants Res 2020 Dec 22;31(12):1199-1206. Epub 2020 Sep 22.

Clinic of Reconstructive Dentistry, University of Zurich, Zurich, Switzerland.

Aim: To assess changes in the position of the mucogingival junction (MGJ) after an apically positioned flap (APF) with collagen matrix performed at sites with or without previous guided bone regeneration (GBR).

Materials And Methods: Dental implants were placed with or without GBR (group GBR or non-GBR) depending on the available ridge width in 30 patients with a limited width of keratinized mucosa (MGJ placed more coronally than the expected prosthetic margin). An apically positioned flap with collagen matrix was performed in both groups. Changes in the position of the MGJ from the day of an apically positioned flap up to 1, 3, and 12 months thereafter were assessed on digital scans (primary endpoint). Secondary endpoints were the width and thickness of the keratinized mucosa, and the position of the mucosal margin.

Results: The position of the MGJ changed significantly from baseline to the first month, by 5.25 ± 2.10 and 4.40 ± 1.41 mm in groups GBR and non-GBR, respectively. Thereafter, the position remained stable in both groups up to 1 year (changes from baseline of 5.46 ± 2.28 and 4.58 ± 1.92 mm, respectively; p = .34). The position of the mucosal margin did not differ between groups GBR and non-GBR (-1.57 ± 2.04 and -1.75 ± 2.08 mm, respectively; p = .84), nor did the width of the keratinized mucosa (1.20 ± 1.03 and 0.99 ± 0.66 mm, p = .91) or its thickness (1.28 ± 0.44 and 1.40 ± 0.78 mm, p = .87).

Conclusion: Apically positioned flap combined with a collagen matrix results in a more apical position of the MGJ at sites with or without GBR. Following a coronal shift during the first month after the apical positioning of the flap, the level of the MGJ remained stable.
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http://dx.doi.org/10.1111/clr.13665DOI Listing
December 2020

Clinical factors influencing implant positioning by guided surgery using a nonmetal sleeve template in the partially edentulous ridge: Multiple regression analysis of a prospective cohort.

Clin Oral Implants Res 2020 Dec 22;31(12):1187-1198. Epub 2020 Sep 22.

Department of Periodontology, Research Institute for Periodontal Regeneration, Yonsei University College of Dentistry, Seoul, Korea.

Objective: To determine the positional accuracy of implants placed with a three-dimensionally printed template having nonmetal sleeves and to determine the contributing factors to observed deviations.

Materials And Methods: One hundred and eighty-seven implants placed in 72 patients were analyzed. Presurgical intraoral scans and cone-beam computed tomography images obtained before and after surgery were superimposed, and vertical, angular, platform, and apex deviations were measured between the virtually planned and actually placed positions. A multiple linear regression model was designed for identifying the contributing factors. Statistical significance was set at p < .05, with Bonferroni correction if necessary (p < .0167).

Results: A total of 187 implants demonstrated deviations of 0.65 [0.56, 0.75] mm (mean [95% confidence interval]) vertically, 3.59° [3.30°, 3.89°] angularly, 1.16 [1.04, 1.28] mm at platform, and 1.50 [1.36, 1.65] mm at apex. Implants placed in the mandible showed larger angular, platform, and apex deviations compared with those in the maxilla (p = .049, p = .014 and p = .003, respectively). Implants placed at the third or fourth nearest sites from the most-distal tooth had larger deviations than those placed at the first or second nearest sites, in vertical, platform, and apical aspects (p = .015, p = .011 andp = .018, respectively). This was only applicable to free-ending-supported templates (p < .0167), and anchor pin-supported free-ending templates (p < .0167).

Conclusion: Using a three-dimensionally printed surgical template with a nonmetal sleeve in the partial edentulous ridge resulted in larger deviations in implants placed in the mandible or distal free-end third or fourth nearest site.
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http://dx.doi.org/10.1111/clr.13664DOI Listing
December 2020

Effects of Scanning Strategy and Scanner Type on the Accuracy of Intraoral Scans: A New Approach for Assessing the Accuracy of Scanned Data.

J Prosthodont 2020 Jul 26;29(6):518-523. Epub 2020 Jun 26.

Professor, Department of Prosthodontics, Yonsei University College of Dentistry, Seoul, Republic of Korea.

Purpose: This study aimed to determine the most reliable scanning strategy and scanner type, using a new protocol for assessing the accuracy (trueness and precision) of intraoral scan data.

Materials And Methods: Five different maxillary and mandibular typodont pairs (n = 10) and 2 intraoral scanners were used for the study. A reference scan for each arch was obtained with an industrial scanner. Scanning strategies were classified into 2 continuous methods-continuous scan in horizontal direction (CH group) and continuous scan with vertical rotation in anterior region (CV group)-and 1 segmental method (S group). In the CH group, the scanner head was maintained mostly in a horizontal position. In the CV group, the scanners were rotated 180° around the anterior tooth region to allow smooth scanning through the area. The intraoral scan data were individually superimposed over their corresponding reference scan data. Raw data of the distances between paired surface points were extracted from the superimposed pairs of datasets, with (original distance values) or without consideration (absolute distance values) of the value signs. Trueness values were calculated using absolute distance values, while precision values were obtained from original distance values. Data were analyzed with a 2-way repeated-measures analysis of variance using α = 0.05 as the level of significance.

Results: The CV group produced significantly inferior outcomes compared to the CH and S groups in terms of trueness (p < 0.001, F = 24.67), whereas no significant differences were observed among the 3 scanning strategies with respect to precision (p = 0.451, F = 0.83). Scanner type did not produce significant differences in terms of either trueness (p = 0.058, F = 4.72) or precision (p = 0.742, F = 0.12).

Conclusions: The segmental approach for scanning the region of interest first and continuous scanning with the scanner head held mostly in a horizontal position are both acceptable as full-arch scanning strategies. However, vertical rotation of intraoral scanners should be minimized.
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http://dx.doi.org/10.1111/jopr.13158DOI Listing
July 2020

Wear resistance of 3D-printed denture tooth resin opposing zirconia and metal antagonists.

J Prosthet Dent 2020 Sep 27;124(3):387-394. Epub 2019 Nov 27.

Associate Professor, Division of Prosthodontics, Department of Dentistry, Asan Medical Center, College of Medicine, University of Ulsan, Seoul, Republic of Korea. Electronic address:

Statement Of Problem: Additive manufacturing technology can be used for denture bases and also denture teeth. Therefore, the mechanical properties of 3D-printed resin denture teeth should be evaluated.

Purpose: The purpose of this in vitro study was to compare the wear resistance of 3D-printed denture tooth resin with that of conventionally prefabricated denture teeth.

Material And Methods: Eighty substrate specimens were prepared with 5 kinds of resin denture teeth: 3D-printed denture tooth resin (DENTCA denture tooth resin; DENTCA, Inc), Artic 6 (Kulzer GmbH), Preference (Candulor AG), Premium 6 (Kulzer GmbH), and Surpass (GC Corp). The 3D-printed denture tooth specimens were made of methacrylate-based photopolymerized resin by stereolithography 3D printing. Antagonistic surfaces were made from zirconia by milling and from cobalt-chromium (Co-Cr) alloy by 3D printing and casting. The specimens were loaded at 49 N for 30 000 cycles under thermocycling conditions in a mastication simulator. Wear resistance was measured by calculating the volume of substance lost. Wear surface characteristics were observed by using a scanning electron microscope (SEM). Two-way ANOVA was used to analyze the data (α=.05).

Results: The influence of the resin denture teeth and the type of antagonist were both statistically significant. The wear volume loss of the 3D-printed denture tooth resin was higher than that of Artic 6 and Preference when opposing the zirconia and the metal antagonists (P<.05). The 3D-printed denture tooth resin did not show a significant difference from Premium 6 with the zirconia and the metal antagonists or Surpass with the zirconia antagonist. From the SEM images, the specimens of the 3D-printed denture tooth resin showed a relatively smooth surface with the zirconia antagonist and exhibited cracks when opposed by the metal antagonist.

Conclusions: The results suggest that 3D-printing by using resin materials provides adequate wear resistance for denture tooth use.
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http://dx.doi.org/10.1016/j.prosdent.2019.09.004DOI Listing
September 2020

Trueness of digital intraoral impression in reproducing multiple implant position.

PLoS One 2019 19;14(11):e0222070. Epub 2019 Nov 19.

Department of Prosthodontics, Yonsei University, College of Dentistry, Seoul, South Korea.

The aim of this study was to evaluate the trueness of 5 intraoral scanners (IOSs) for digital impression of simulated implant scan bodies in a partially edentulous model. A 3D printed partially edentulous mandible model made of Co-Cr with a total of 6 bilaterally positioned cylinders in the canine, second premolar, and second molar area served as the study model. Digital scans of the model were made with a reference scanner (steroSCAN neo) and 5 IOSs (CEREC Omnicam, CS3600, i500, iTero Element, and TRIOS 3) (n = 10). For each IOS's dataset, the XYZ coordinates of the cylinders were obtained from the reference point and the deviations from the reference scanner were calculated using a 3D reverse engineering program (Rapidform). The trueness values were analyzed by Kruskal-Wallis test and Mann-Whitney post hoc test. Direction and amount of deviation differed among cylinder position and among IOSs. Regardless of the IOS type, the cylinders positioned on the left second molar, nearest to the scanning start point, showed the smallest deviation. The deviation generally increased further away from scanning start point towards the right second molar. TRIOS 3 and i500 outperformed the other IOSs for partially edentulous digital impression. The accuracy of the CEREC Omnicam, CS3600, and iTero Element were similar on the left side, but they showed more deviations on the right side of the arch when compared to the other IOSs. The accuracy of IOS is still an area that needs to be improved.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0222070PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6863547PMC
March 2020

GABARAPs and LC3s have opposite roles in regulating ULK1 for autophagy induction.

Autophagy 2020 04 28;16(4):600-614. Epub 2019 Jun 28.

Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN, USA.

ULK1 (unc-51 like autophagy activating kinase 1) is the key mediator of MTORC1 signaling to macroautophagy/autophagy. ULK1 functions as a protein complex by interacting with ATG13, RB1CC1/FIP200, and ATG101. How the ULK1 complex is regulated to trigger autophagy induction remains unclear. In this study, we have determined roles of Atg8-family proteins (ATG8s) in regulating ULK1 activity and autophagy. Using human cells depleted of each subfamily of ATG8, we found that the GABARAP subfamily positively regulates ULK1 activity and phagophore and autophagosome formation in response to starvation. In contrast, the LC3 subfamily negatively regulates ULK1 activity and phagophore formation. By reconstituting ATG8-depleted cells with individual ATG8 members, we identified GABARAP and GABARAPL1 as positive and LC3B and LC3C as negative regulators of ULK1 activity. To address the role of ATG8 binding to ULK1, we mutated the LIR of endogenous ULK1 to disrupt the ATG8-ULK1 interaction by genome editing. The mutation drastically reduced the activity of ULK1, autophagic degradation of SQSTM1, and phagophore formation in response to starvation. The mutation also suppressed the formation and turnover of autophagosomes in response to starvation. Similar to the mutation of the ULK1 LIR, disruption of the ATG13-ATG8 interaction suppressed ULK1 activity and autophagosome formation. In contrast, RB1CC1 did not show any specific binding to ATG8s, and mutation of its LIR did not affect ULK1 activity. Together, this study demonstrates differential binding and opposite regulation of the ULK1 complex by GABARAPs and LC3s, and an important role of the ULK1- and ATG13-ATG8 interactions in autophagy induction. ATG5: autophagy related 5; ATG7: autophagy related 7; ATG8: autophagy related 8; ATG13: autophagy related 13; ATG14: autophagy related 14; ATG16L1: autophagy related 16 like 1; ATG101: autophagy related 101; BAFA1: bafilomycin A; BECN1: beclin 1; Cas9: CRISPR associated protein 9; CRISPR: clustered regularly interspaced short palindromic repeats; EBSS: earle's balanced salt solution; DAPI: 4'-6-diamidino-2-phenylindole; GABARAP: GABA type A receptor-associated protein; GABARAPL1: GABA type A receptor-associated protein like 1; GABARAPL2: GABA type A receptor-associated protein like 2; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescence protein; gRNA: guide RNA; KI: kinase inactive mutant; KO: knockout; LC3A: microtubule associated protein 1 light chain 3 alpha; LC3B: microtubule associated protein 1 light chain 3 beta; LC3C: microtubule associated protein 1 light chain 3 gamma; LIR: LC3-interacting region; MTORC1: mechanistic target of rapamycin kinase complex 1; PBS: phosphate buffered saline; PCR: polymerase chain reaction; PE: phosphatidylethanolamine; PtdIns3P: phosphatidylinositol-3-phosphate; qPCR: quantitative PCR; RB1CC1/FIP200: RB1 inducible coiled-coil 1; RPS6KB1: ribosomal protein S6 kinase B1; SEM: standard error of the mean; SQSTM1/p62: sequestosome 1; TALEN: transcription activator-like effector nuclease; TUBA: tubulin alpha; ULK1: unc-51 like autophagy activating kinase 1; WB: western blotting; WIPI2: WD repeat domain phosphoinositide interacting 2; WT: wild type.
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http://dx.doi.org/10.1080/15548627.2019.1632620DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7138202PMC
April 2020

Measuring the Complete-arch Distortion of an Optical Dental Impression.

J Vis Exp 2019 05 30(147). Epub 2019 May 30.

Department of Prosthodontics, College of Dentistry, Yonsei University.

Digital workflows have actively been used to produce dental restorations or oral appliances since dentists started to make digital impressions by acquiring 3D images with an intraoral scanner. Because of the nature of scanning the oral cavity in the patient's mouth, the intraoral scanner is a handheld device with a small optical window, stitching together small data to complete the entire image. During the complete-arch impression procedure, a deformation of the impression body can occur and affect the fit of the restoration or appliance. In order to measure these distortions, a master specimen was designed and produced with a metal 3D printer. Designed reference geometries allow setting independent coordinate systems for each impression and measure x, y, and z displacements of the cylinder top circle center where the distortion of the impression can be evaluated. In order to evaluate the reliability of this method, the coordinate values of the cylinder are calculated and compared between the original computer-aided design (CAD) data and the reference data acquired with the industrial scanner. The coordinate differences between the two groups were mostly less than 50 µm, but the deviations were high due to the tolerance of 3D printing in the z coordinates of the obliquely designed cylinder on the molar. However, since the printed model sets a new standard, it does not affect the results of the test evaluation. The reproducibility of the reference scanner is 11.0 ± 1.8 µm. This test method can be used to identify and improve upon the intrinsic problems of an intraoral scanner or to establish a scanning strategy by measuring the degree of distortion at each part of the complete-arch digital impression.
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http://dx.doi.org/10.3791/59261DOI Listing
May 2019

Comparative reproducibility analysis of 6 intraoral scanners used on complex intracoronal preparations.

J Prosthet Dent 2020 Jan 23;123(1):113-120. Epub 2019 Apr 23.

Professor, Department of Prosthodontics, Yonsei University, College of Dentistry, Seoul, Republic of Korea. Electronic address:

Statement Of Problem: Although studies have reported the trueness and precision of intraoral scanners (IOSs), studies addressing the accuracy of IOSs in reproducing inlay preparations are lacking.

Purpose: The purpose of this in vitro study was to compare the accuracy of representative IOSs in obtaining digital scans of inlay preparations and to evaluate whether the IOSs had sufficient depth of field to obtain accurate images of narrow and deep cavity preparations.

Material And Methods: Digital scans of a bimaxillary typodont with cavity preparations for inlay restorations on the maxillary first premolar, first and second molar, mandibular second premolar, and first molar were obtained using 6 IOSs (CEREC Omnicam, E4D, FastScan, iTero, TRIOS, and Zfx IntraScan). Standard tessellation language (STL) data sets were analyzed using the 3-dimensional analysis software (Geomagic Verify). Color-coded maps were used to compare the magnitude and pattern of general deviation of the IOSs with those of a reference scan. Each tooth prepared for inlay restoration was digitally cut out, and the trueness and precision of each IOS were measured using the superimposition technique. Statistical analyses were conducted using statistical software (α=.05).

Results: The trueness values were lowest with the FastScan (22.1 μm), followed by TRIOS (22.7 μm), CEREC Omnicam (23.2 μm), iTero (26.8 μm), Zfx IntraScan (36.4 μm), and E4D (46.2 μm). In general, the digital scans of more complicated cavity design showed more deviation. Color-coded maps showed positive vertical discrepancy with the E4D and negative vertical discrepancy with the Zfx IntraScan, especially on the cavity floor. Regarding precision, the highest value was observed in the E4D (37.7 μm), while the lowest value was observed with the TRIOS (7.0 μm). However, no significant difference was found between teeth with different inlay preparations. Scanning errors were more frequently seen in the cervical area.

Conclusions: Different IOSs and types of cavity design influenced the accuracy of the digital scans. Scans of more complex cavity geometry generally showed higher deviation. The E4D exhibited the most deviation in both trueness and precision, followed by the Zfx IntraScan. The E4D and Zfx IntraScan appeared to have less depth of field than the others to obtain digital scans for inlay preparation with different heights.
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http://dx.doi.org/10.1016/j.prosdent.2018.10.025DOI Listing
January 2020

Assessment of metal sleeve-free 3D-printed implant surgical guides.

Dent Mater 2019 03 23;35(3):468-476. Epub 2019 Jan 23.

Department of Prosthodontics/Oral Science Research Center, Yonsei University College of Dentistry, Seoul, Republic of Korea. Electronic address:

Objectives: The aim of the present study was to investigate the adaptation and guide hole tolerance of metal sleeve-free computer-assisted implant surgical guides fabricated with 3D printers.

Methods: An implant surgical guide for full-guided implant placement was designed with a total of eight different guide holes. Ten implant surgical guides (n=10) were fabricated from the same design with each of five in-office 3D printers (D1, FOR, ONE, PER, and ZEN) using compatible printing materials. Ten surgical guides fabricated by the manufacturer of the implant company were used as the control group (CON). The adaptation of the surgical guides was evaluated by the replica technique. The tolerance of the guide holes was evaluated by measuring the degree of diversion with guide drills.

Results: CON and D1 showed superior internal adaptation with a gap distance of less than 1mm. The mean degree of diversion of the guide holes ranged from 3.45° for ZEN to 6.55° for PER. The tolerances of CON (4.70°) and D1 (4.50°) did not differ at the level of statistical significance at α=0.05.

Significance: The characteristics of implant surgical guides were evaluated per se. None of the 3D printers fabricated superior implant surgical guides to those produced by the manufacturer with regard to the internal fit and guide tolerance. However, the potential for the routine clinical use of in-office 3D printers was demonstrated. Further studies are required to determine how the guide hole tolerance and the angular deviation between the preplanned and actual implant positions are related.
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http://dx.doi.org/10.1016/j.dental.2019.01.001DOI Listing
March 2019

Integration of intraoral digital scans with a 3D facial scan for anterior tooth rehabilitation.

J Prosthet Dent 2019 Mar 31;121(3):394-397. Epub 2018 Oct 31.

Professor, Department of Prosthodontics, College of Dentistry, Yonsei University, Seoul, Republic of Korea. Electronic address:

This article describes a digital technique that combines intraoral digital scans with a 3-dimensional facial scan to predict the outcome of prosthodontic treatment of anterior teeth at the treatment planning phase. This approach may increase patient acceptance of the definitive treatment, as the altered facial appearance is visualized with definitive prosthodontic restorations, thereby improving communication before treatment begins.
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http://dx.doi.org/10.1016/j.prosdent.2018.03.018DOI Listing
March 2019

3D Printing of Resin Material for Denture Artificial Teeth: Chipping and Indirect Tensile Fracture Resistance.

Materials (Basel) 2018 Sep 21;11(10). Epub 2018 Sep 21.

Division of Prosthodontics, Department of Dentistry, Asan Medical Center, College of Medicine, University of Ulsan, 88 Olympic-ro 43-gil, Songpa-gu, Seoul 05505, Korea.

3D printing of denture artificial teeth with resin materials is worthy of study in a novel way. This study evaluated chipping and indirect tensile fracture resistance of 3D printing resin material (Dentca 3D printing denture teeth resin) compared with conventionally prefabricated resin denture teeth (Premium-8, Surpass, SR-Orthosit-PE, and Preference). One hundred tooth specimens were prepared for testing. The 3D printed tooth specimens were printed at a 50 µm layer thickness with methacrylate-based photopolymerized resin by stereolithography 3D printing. Chipping and indirect tensile fracture tests were conducted at a speed of 1 mm/min until fracture. The indirect tensile fracture loads of the 3D printed resin teeth were higher than those of Premium-8, Surpass, and SR-Orthosit-PE, and lower than those of Preference teeth. Regarding chipping resistance, the 3D printed resin teeth were not different from Surpass and SR-Orthosit-PE, and were lower than Premium-8 and Preference teeth. The 3D printed resin teeth exhibited vertical fracture of the loaded cusp without deformation in chipping. The 3D printed resin teeth showed simultaneous fracture of two cusps in indirect tensile fracture, unlike other teeth. The results of this study suggest that 3D printing technology using resin materials provides adequate fracture resistance for denture artificial tooth use.
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http://dx.doi.org/10.3390/ma11101798DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6213768PMC
September 2018

Precision of digital implant models compared to conventional implant models for posterior single implant crowns: A within-subject comparison.

Clin Oral Implants Res 2018 Sep 30;29(9):931-936. Epub 2018 Aug 30.

Clinic of Fixed and Removable Prosthodontics and Dental Material Science, Center of Dental Medicine, University of Zurich, Zurich, Switzerland.

Objective: To calculate the precision of the implant analog position in digital models generated from different computer-assisted design and computer-assisted manufacturing (CAD-CAM) systems compared to gypsum models acquired from conventional implant impressions.

Materials And Methods: In five patients in need of a single implant crown, a within-subject comparison was performed applying four different manufacturing processes for the implant model. Each implant was scanned with three different intraoral scanners: iTero Cadent (ITE), Lava True Definition (LTD), and Trios 3Shape (TRI). All digital implant models were fabricated using the corresponding certified CAD-CAM workflow. In addition, a conventional impression was taken (CON) and a gypsum model fabricated. Three consecutive impressions were acquired with each impression system. Following fabrication, all implant models were scanned. The datasets were aligned by a repeated best-fit algorithm and the precision for the implant analog and the adjacent teeth was measured. The precision served as a measure for reproducibility.

Results: Mean precision values of the implant analog in the digital models were 57.2 ± 32.6 µm (ITE), 88.6 ± 46.0 µm (TRI), and 176.7 ± 120.4 µm (LTD). Group CON (32.7 ± 11.6 µm) demonstrated a statistically significantly lower mean precision value for the implant position in the implant model as compared to all other groups representing a high reproducibility. The mean precision values for the reference ranged between 31.4 ± 3.5 µm (TRI) and 39.5 ± 16.5 µm (ITE). No statistical significant difference was calculated between the four treatment groups.

Conclusions: The conventional implant model represented the greatest reproducibility of the implant position. Digital implant models demonstrated less precision compared to the conventional workflow.
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http://dx.doi.org/10.1111/clr.13349DOI Listing
September 2018

Digital workflow to provide an immediate interim restoration after single-implant placement by using a surgical guide and a matrix-positioning device.

J Prosthet Dent 2019 Jan 7;121(1):17-21. Epub 2018 Aug 7.

Professor, Department of Prosthodontics, College of Dentistry, Yonsei University, Seoul, Republic of Korea. Electronic address:

This article describes a workflow based on a top-down approach to provide a fixed-type immediate interim restoration after placing a single implant using a digitally driven surgical guide and a matrix-positioning device. A characteristic of the technique is that both the surgical guide and the matrix-positioning device are fabricated from a single diagnostic virtual trial restoration designed on computer-aided design (CAD) software. This workflow may shorten the time required for chairside placement of an interim restoration and enhance esthetics when rehabilitating anterior teeth.
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http://dx.doi.org/10.1016/j.prosdent.2018.03.029DOI Listing
January 2019

Accuracy of 9 intraoral scanners for complete-arch image acquisition: A qualitative and quantitative evaluation.

J Prosthet Dent 2018 Dec 10;120(6):895-903.e1. Epub 2018 Jul 10.

Professor, Department of Prosthodontics, Yonsei University, College of Dentistry, Seoul, Republic of Korea.

Statement Of Problem: Different intraoral scanners (IOSs) are available for digital dentistry. However, information on the accuracy of various IOSs for complete-arch digital scans is limited.

Purpose: The purpose of this in vitro study was to evaluate the trueness and precision of complete-arch digital scans produced by 9 IOSs, using the superimposition method, and to compare them based on characteristics including the data capture principle and mode and the need for powder coating.

Material And Methods: Nine IOSs were used to obtain standard tessellation language (STL) data for a bimaxillary complete-arch model with various cavity preparations (N=10). The scanning performance was evaluated quantitatively and qualitatively. For quantitative evaluation, the images were processed and analyzed using 3-dimensional (3D) analysis software. After we superimposed the datasets, trueness was obtained by comparing it with the reference scan, and precision was obtained from intragroup comparisons. The IOSs were compared based on the data capture principle and mode and the need for powder coating. Statistical analyses were conducted using a Kruskal-Wallis test, followed by multiple Mann-Whitney U tests for pairwise comparisons among groups (α=.05). For qualitative evaluation, surface smoothness and sharp edge reproducibility of the digital images were compared.

Results: The median precision values were lowest in the TRIOS model (average, 34.70 μm; maximum, 263.55 μm) and highest in the E4D model (average, 357.05 μm; maximum 2309.45 μm). Median average trueness values were lowest in the TRIOS model (42.30 μm) and highest in the Zfx IntraScan model (153.80 μm). The CS 3500 model had the lowest median maximum trueness values (450.75 μm); the E4D model had the highest values (2680.55 μm). Individual image and video sequence data captures showed similar median average trueness values (P>.05); the median maximum values of individual images were higher than those of the video sequence (P<.05). Swept source optical coherence tomography (SS-OCT) exhibited higher trueness values than those of other scanning principles (P<.05). The FastScan and True Definition, which require powder coating, showed significantly better trueness than other IOSs that did not require powdering (P<.05). The E4D, PlanScan, and Zfx IntraScan models had an increased tendency to produce images with imperfect surface features and to round off sharp edges.

Conclusions: The E4D and Zfx IntraScan models did not perform as accurately as the other IOSs. The data capture principle of SS-OCT and the mode of individual image acquisition exhibited inferior trueness. The FastScan and True Definition, which require powder coating, exhibited better trueness. The qualitative aspects of the IOSs varied in terms of polygon shapes, sharp edge reproducibility, and surface smoothness.
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http://dx.doi.org/10.1016/j.prosdent.2018.01.035DOI Listing
December 2018

Wear Resistance of 3D Printing Resin Material Opposing Zirconia and Metal Antagonists.

Materials (Basel) 2018 Jun 20;11(6). Epub 2018 Jun 20.

Division of Prosthodontics, Department of Dentistry, Asan Medical Center, College of Medicine, University of Ulsan, 88 Olympic-ro 43-gil, Songpa-gu, Seoul 05505, Korea.

3D printing offers many advantages in dental prosthesis manufacturing. This study evaluated the wear resistance of 3D printing resin material compared with milling and conventional resin materials. Sixty substrate specimens were prepared with three types of resin materials: 3D printed resin, milled resin, and self-cured resin. The 3D printed specimens were printed at a build angle of 0° and 100 μm layer thickness by digital light processing 3D printing. Two kinds of abraders were made of zirconia and CoCr alloy. The specimens were loaded at 5 kg for 30,000 chewing cycles with vertical and horizontal movements under thermocycling condition. The 3D printed resin did not show significant difference in the maximal depth loss or the volume loss of wear compared to the milled and the self-cured resins. No significant difference was revealed depending on the abraders in the maximal depth loss or the volume loss of wear. In SEM views, the 3D printed resin showed cracks and separation of inter-layer bonds when opposing the metal abrader. The results suggest that the 3D printing using resin materials provides adequate wear resistance for dental use.
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http://dx.doi.org/10.3390/ma11061043DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6025067PMC
June 2018
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